Aircraft cabin pressure regulating means



May 4, 1948.

W. D. TEAGUE, JR

AIRCRAFT CABIN PRESSURE REGULATING KENS 5 Sheets-Sheet 1;

Filed Feb. 26, 1944 6VOUO 8838 o o o INVENTOR. mlfier Iague AE:

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AIRCRAFTCABIN PRESSURE REGULATING MEANS Filed Feb. 26, 1944 5 Sheets-Sheet 2 I N VEN TOR.

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AIRCRAFT CABIN PRESSURE REGULATING MEANS Filed Feb. 26, 1944 5 Sheets-Sheet ,4'

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w.. D. TEAGUE, JR I AIRCRAFT CABIN PRESSURE azeum'r'me was Filed Feb 26, 1944' 5 Shqets-Shee? 5 u n 6 ml WM INVENTOR.

HTTORA/EY Patented May 4,1948

AIRCRAFT CABIN PRESSURE REGULATING MEANS Walter D. Teague, .ln, Alpine, N. 3., assignor to Bendix Aviation Corporation, Teterboro, N. 3., a corporation of Delaware Application February 26, 1944, Serial No. 524,063

13 Claims.

This invention relates to novel and improved control means and methods for maintaining air at suitable pressures in a closed or sealed compartment of an aircraft and more particularly to improvements in an air outlet control mechanism and valve of a type such as shown, for

example, in the U. S..Patent No. 2,002,057 to Gregg, dated May 21, 1935, and owned by the assignee of the present invention.

Heretofore there has been employed a form of outlet control having a conoidal sectional valve seating on a venturi as a variable restriction to outlet how and such valves have in turn been connected by a tube or rod to an air motor piston or control means.

An object of the present invention is to provide an outlet control valve having a nozzle with an area normal to the airstream, progressively decreasing so as to smoothly accelerate the airflow, and arranged as a valve seat for a cylindrical gate valve cooperating therewith, which valve forms a part of an air motor piston.

Another object of my invention is to provide a critical airflow orifice arranged to operate under aircraft conditions without a down stream or recovery cone and having a cylindrical gate valve with a sharp knife-like circular edge provided at one end for engaging the side wall of the orifice for closing the same.

An advantage in the latter form of my cylindrical gate valve is the inherent stability which is secured at the valve, by the knife-like edge acting on the nozzle as a seat. It is apparent from such an arrangement that there is no valve area to speak of in the region of high velocity and hence no tendency to close the valve with increased fiow velocity as is true in valves heretofore known in the prior art.

Another object of my invention is to provide novel methods for controlling the pressures within an aircraft cabin so as to maintain predetermined cabin pressures for varying atmospheric pressure conditions. J

Another object of my invention is to provide in combination a novel valve [for controlling the flow of air from an aircraft cabin, the valve being so arranged that the airflow forces acting upon the same will be relatively small and the same including a piston and a pressure chamber having a bleed orifice therein, whereby the piston may serve as an actuating means for the valve and as a cushioning or dampening means for the air forces acting upon the valve so that accurate adjustment of the valve may be effected without the necessity of a follow-up means.

Another object of my invention is to provide a novel control mechanism, whereby there is provided a control piston open at one side to cabin pressure and a fixed jet communicating between DEC 18 1951 the other side of the control piston and the atmosphere, while an evacuated bellows acted upon by cabin pressure opens and closes a. valve controlling a variable orifice so as to open the said other side of the control piston to cabin pressure, the said arrangement including a main spring tension means which acts upon the piston 50 as to provide proportional regulation between the controlling bellows and the piston. Another object of my invention is to provide in the aforenoted control mechanism a novel differential control bellows which has provided cabin pressure and atmospheric pressure acting thereon in such a manner as to control a second variable orifice so as to provide a maximum diflferential control. Another object of my invention range the above control bellows that as the maximum differential between cabin and atmospheric pressure is reached the differential bellows begins automatically to regulate, overpowering the constant pressure control bellows which opens its variable orifice all the way and acts from then on as a fixed jet. Such an arrangement has a decided advantage over the control. mechanisms heretofore known, since the differential bellows and its spring may be made as sensitive as required and the amount of maximum dliierential may be controlled to a close degree with little difl'erence between high and low flow. Here again the bellows may be arranged in direct communication with its variable orifice without a friction increasing interseal. 7

Another object of my invention is to provide a similar control mechanism whereby a constant ratio between cabin pressure and atmospheric pressure may be obtained and which control is practically identical with the constant differential control with the exception that two concentric bellows are employed, the ratio of their areas determining the maximum ratio.

Another object of my invention is to provid a control mechanism having a minimum of friction and inertia plus proper air dampening which will obviate the necessity for separate follow-up action in the valve. Thus under my present invention there is no need for a separate mechanical linkage or other follow-up arrangement which must necessarily interfere with the accuracy of operations Another object of my invention is to provide a control valve, whereby there may be utilized an emergency manual control means by which the pilot or crew member may mechanically set the position of the main valve at any time, and lock the same in such adjusted position so as to thereby permit completion of a mission or flight requiring supercharged cabin operation in the event of failure of the control valve.

A further object of my invention is to provide istosoar- A accrues a control mechanism of the utmost simplicity of construction and operation avoiding the use of wearing parts such as levers, linkages, and sliding seals so as to minimize the possibility of fail:- ure in service.

A further object of my invention is to provide a control mechanism which is inherently stable in operation and arranged so that regulation takes place at any altitude and with complete absence from hunting.

The above and further obiects and novel features of this invention will more fully appear from the following detailed description and the accompanying drawings wherein like reference characters refer to like parts in the several views. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not designed as a definition of the limits of'the invention, reference being had for this purpose to the appended claims.

In the drawings:

Figure 1 is an assembled view of my control mechanism showing the same as attached to a cabin wall of an aircraft.

Figure 2 is a perspective view illustrating the control valve and showing in perspective the nozzle detached therefrom.

Figure 3 is a top plan view of the control mechanism.

Figure 4. is a plan view of the mechanism with the top covers removed and showing the interior of the pressure chambers of the control bellows.

Figure 5 is a sectional view of Figure 1 taken along the lines 5-5 and showing the differential control mechanism.

Figure 6 is a sectional view looking in an opposite direction from Figure 5 and illustrating a second form of my invention in which there is shown the constant ratio control mechanism.

Figure 7 is a fragmentary sectional view of the emergency manual control showing the same in an inoperative position.

Figure 8 is a fragmentary sectional view similar to Figure 7 with the emergency manual control in operating position.

Figure 9 is a perspective view of the emergency manual control.

In Figure 1 the invention is shown in an assembled view as attached to the cabin wall ll of an aircraft. Air is preferably conducted under pressure into the cabin by a supercharger or other suitable means which may be driven in the conventional manner by an aircraft engine, electrical drive, hydraulic drive, or by a turbo bleed or in any other manner well known in the art. m shown in Figure 5 the nozzle indicated by numeral I8 is attached to the wall of a cabin ll through suitable bolts 12. An opening Il may be formed in the wall of the cabin, cooperating with an orifice ll of the nozzle I01 A casing I5 is attached to the nozzle III by the bolts l2 and by other suitable bolts indicated by the numeral As best indicated in Figure 5 there is provided within the casing IS a central shaft or stationary plug l1 formed integral with a wall portion 23 of the casing l5 and positioned concentric with the nozzle opening l3. There is affixed at the free end of the shaft I! a conical shaped member l9, which may be fastened in place by a screw 20.

As shown in Figures 2, 5 and 6 nozzle l0 includes an annular member IDA having a flared surface which rises progressively from a circum- 4 ferential edge IOB to a point "C and then progressively'desoends into an annular orifice M to form a sink-like nozzle. The nozzle surface is designed for the full rated maximum flow of air with the conical shaped member is sufilciently spaced from the surface of the nozzle proper for such flow and with the area normal to the stream progressively decreasing from the outer circumferential edge [013 to the inner annular orifice i4 so as to smoothly accelerate the airflow from the circumferential edge 183 into the orifice Hi. The surface of the nozzle is so gently curved that the flow does not break away or burble. Thus the design permits the nozzle to fill or flow full (1. e., the airstream fills the section) so as to pass the maximum amount of air for a. given size of nozzle.

Slidably mounted on the member l9 and iongitudinally movable thereon is a cylindrical gate valve 2! having a knife-like edge 22 which is adapted to contact the surface of the nozzle It at an acute angle so as to control the fiow of air from the cabin. Fixed to the cylinder 2| is a piston member 22 which provides a servo motor means for operating the valve 2!. A spring 23 is interposed between the piston member 22 and the wall l8 of the casing 15 so as to bias the piston 22 and the cylindrical gate valve 21 in a direction towards the nozzle [0. Between the piston 22 and the nozzle III is a chamber indicated by the numeral 24 and defined by the surface of the nozzle l0, piston 22 and the casing l5. Surrounding a portion of the chamber 24 is a screen indicated by the numeral 25 and having formed therein suitable openings 26 leading into the cabin. Thus it will be seen that the pressure within the cabin acting through openings 26 acts upon the piston 22 in a direction opposing the biasing force of the spring 23. At the opposite side of the piston 22 is a second chamber indicated by the numeral 2'! and defined by the cas ing l5, wall l8 and piston 22. The wall 18 has formed therein suitable orifices leading from the cabin to the atmosphere as will be explained.

Formed within the casing l5 are chambers 28 and 29 defined by easing l5, wall l8, walls 38 and 3|, and cover plates 32 and 33 fastened to 'the casing i5 by suitable bolts as indicated in Figures 5 and 6. The chamber 28 opens into the cabin through a suitable screened opening 34 formed in the cover plates 32. Mounted within the chamber 28 is a suitable evacuated bellows indicated by the numeral 35 having a spring 36 biasing the same to an expanded position against the pressure of the cabin. The bellows 35 is suspended with the chamber 28 by an adjustable bolt 31 screw-threadedly engaged in the top member 32. The screw 31 has formed therein a cleft 31A, as shown in Figure 3, whereby the same may be conveniently adjusted by a screw driver or other suitable means from the exterior of the casing for adjusting the position of the bellows 35. An orifice' 38 leads from the chamber 28 into the chamber 21. The orifice is controlled by a valve 38, biased into a closed position by a spring 40, held in position by a supporting nut actuate the valve 39 so as to open the orifice 39 and permit the flow of cabin pressure from the chamber 28 through the orifice 38 into the chamber 21 so as to aid the biasing force exerted by the spring 23in acting upon the piston 22. Thus the pressure exerted within the chamber 21 acts upon the piston 22 in opposition to cabin pressure acting on the piston at the opposite side thereof at the chamber 24. An orifice or fixed jet indicated by the numeral 44 leads from the chamber 21 into the chamber 29. The latter orifice 44 is open at all times and serves as a bleed from the chamber 21 into the chamber 29. A conduit 45, Figures 1 and 6, leads from the chamber 21 to the atmosphere and may be connected directly to the atmosphere or to the static pressure connection of a suitable pitot tube. Thus air flow from the cabin entering the chamber 21 acts upon the piston 22 and is then bled off through the bleed 44 to the atmosphere. The cabin pressure is continuously applied through the chamber 28 to the' piston 22 until the adjustment of the cabin pressure to the desired value has been efiected. The bleed 44 is suitably calibrated for the purpose desired.

Mounted within the chamber 29 is a second bellows indicated by the numeral 46 which is suspended in position from a suitable sealing plate 41 which closes the open end of the chamber 29. The sealing plate 41 is held in position by the cover plate 33 in which is formed a suitable screened opening 48. Openings 49 and 50 are formed in the sealing member 41 and lead into the interior of the bellows 46. Thus the interior of the bellows 4B is subject to cabin pressure exerted through the screened opening 48 and openings 49 and 50. The opposite end of the bellows 46 from the plate 4! fits into a cup-like member 5| having a flanged portion 52 engaged by a spring 53. The spring 53 positioned'in the chamber 29 between the wall I8 and flange 52 tends to bias the bell0ws'46 in a direction opposing the cabin pressure acting upon said bellows within the same. A hollow stem 54 carried by the sealing plate 41 is suspended concentrically within the bellows 46 and carries an adjustment screw 55 slidably mounted therein and screwthreadedly engaging a member 56 fastened at the free end of the bellows 46. The adjustment screw 55 projects from the bottom of the cuplike member 5| and is arranged for controlling the operation of a suitable valve 51. The adjustment screw 55 has formed therein a'cleft 55A, whereby the same may be conveniently adjusted by a screw driver or other suitable means inserted through a hole provided in the top plate 33 upon removal of a bolt 53 screw-threadedly engaged in the top plate 33. A second orifice 59 leads from the chamber 29 into the chamber 21 and is controlled by the valve 5'! which is biased into a closed position by a spring 60 held by a nut 6| screw-threadedly engaged upon a screw 62 in which is formed the orifice 59. The valve 51 has a part 63 operably engaged by the screw 55, whereby the expansion and contraction of the bellows 46 may control the opening and the closing of the valve 51 and thus the flow of the fluid medium within the chamber 21 to the atmosphere through the conduit 45. From the foregoing it will be seen that the bellows 43 is acted upon interiorly by cabin pressure and exteriorly by the biasing force of atmospheric pressure and spring 53. Thus opening of the valve 51 may be efiected upon a predetermined differential between cabin and atmospheric pressures.

As shown in Figure 5 the valves 39 and 57 each operate an opening to admit cabin pressure air to or take such air from the chamber 21 of the main piston control 22. In addition the fixed jet 44 of proper calibrated diameter also communicates between the chamber 21 of the main piston control 22 and atmosphere.

From the foregoing it will be readily seen that any sudden fluctuations or changes in the forces acting upon the. piston 22 will be accompanied by an air fiow at a high velocity through the fixed 'jet 44 causing a dampening effect upon any change in the position of the cylindrical gate valve 2|. Thus piston 22 not only serves as an actuating means for the cylindrical gate valve 2|, but also as a cushioning or dampening means for preventing overtravel of the piston in response to sudden fluctuations in the forces acting upon the cylindrical gate valve 2|. This arrangement thus permits Zthe operation of the cylindrical gate valve 2| to be stabilized without the need of a follow-up arrangement.

The main valve or cylindrical gate valve 2|, as explained, rides on the fixed concentric shaft l1 and has a predetermined clearance at its outside diameter. The above control mechanism is so arranged that at altitudes or predetermined atmospheric pressure ranges corresponding, for example, to standard atmospheric pressure at from sea level to 10,000 feet or any other suitable predetermined range, both bellows 35 and 46 are normally contracted and both valves 39 and 51 are held closed by their springs 40 and 50, respectively. The fixed jet 44, however, allows the pressure in the chamber 21 above the main valve control piston 22 to approach atmospheric. and, since there is cabin pressure in the chamber 24 below the main valve control piston, the main valve 2| will remain open with a small diflerential between the cabin and atmospheric pressure.

As the 10,000 foot point or any other predetermined altitude 0r predetermined atmospheric pressure is reached the evacuated bellows 35 has expanded due to lowering cabin pressure until it has started to open its valve 39. The difieren- .tial pressure bellows 46, however, is still con- 10,000 to 18,000 feet for example or any other predetermined range, air is flowing from the cabin, through the evacuated bellows controlled valve 39 to the top of the main valve control piston 22 and through the fixed orifice 44 to atmosphere. Therefore, the pressure above the main valve control piston 22 and hence the position of the main valve 2| depends on the position of the evacuated bellows 35. Too much cabin pressure will tend to contract the evacuated bellows 35 and close its valve 39, cutting down the fiow of cabin pressure air to the top of the main valve control piston 22. As a result, the pressure in chamber 21 above the main valve control piston 22 will tend to approach atmospheric; the main valve 2| will rise, allowing more air to flow from the cabin, thus lowering the-cabin pressure to the desired point. The opposite reactions take place if cabin pressure is too low.

As the airplane climbs, the differential pres sure bellows 46 approaches its valve, 51, due to the i.1creasing difl'erential between cabin and atmosphere, and at about 18,000 feet or any other predetermined pressure range for which the same is calibrated it begins to open its valve 01. As the valve 51 opens, the evacuated bellows I opens its valve 38 in an attempt to maintain 10,000 feet cabin pressure and finally this reaches the full open-position (slightly above 18,000 feet airplane altitude). From here on up the evacuated bellows controlled valve 39 is wide open and acts as a fixed orifice.

The differential bellows 48 now regulates the pressure above the piston 22 ina similar manner to the evacuated bellows. Too great a differential causes the bellows 35 to expand, opening its valve 39, and causing the main valve 2i 'to rise, thus lowering cabin pressure and de- V creasing the difierential to the desired point.

This action is inherently stable inoperation, and regulation takes place at any altitude or atmospheric pressure-at flows as low as onetenth of a pound perminute with complete absence from hunting.

One factor which contributes to the quality of the low flow operation of the present valve is the design of the main valve 2| itself. The use of the sharp edged tube 2| for closing, instead of a mushroom or other type has several distinct advantages.

First, in a valve which has a large surface parallel to the flow'of air, instability is created by the Bernoulli action. As the valve closes, the flow rate increases, lowering the pressure on the n n formedon the 1m member 1| and is valve surface, thus tending to close it still further. The present valve 2| avoids this conditlon since there is practically no surface for the lowered pressure to act upon due to the limited valve surface presented by the sharp edge 22.

Secondly, in the ease of a mushroom type valve, as the same reaches the closed position, it will have the full diiferential of cabin and atmospheric pressure acting across its entire area to keep it closed. This requires a large force to crack open the valve, causing such a valve to asindicatedin adapted to be enlgggleed fastening nut 12, A channel 14 extends longitudinally in the rod 04 and there is engaged in the channel a portion I! of atom 10, which projects through the easing II into the channel 14. The channel 14 extends longitudinally in the rod 04 and has formed at the opposite ends thereof lateral channels I1 and 18 for receiving the part 15, whereby the rod 04 may be turned 180 from the flange 00 so as 'to' disengage the flange 09.

Thus in order to operate the manual control the pilot loosens the knurled locking nut 12 and turns the control knob 05 180 from the position shown iii-Figure 7 and then adjusts the rod so as to engage the flange 6! as shown in Figure 8,

.after which he may raise or lower the valve 2! to any desiredposition. If he desires to lock the valve in a particular position it is only necessary to tighten the knurled locking nut 12. Disengagement is secured by retracting the rod 85 to the limit of movement and then turning the same 180 so as to disengage the flange 80 as viewed in Figure 'l.

The valve may be installed as explained on any pressure wall or floor of the aircraft cabin and will operate in any position. Installation on a vertical wall will mean that the parts are less afiected by accelerations although this effect will not be greatinanycese.

In Figure 6 there is shown a second form of my invention in which there is provided means for jump open far past the desired point. The present valve 2 I v has the differential pressure of cabin and atmosphere, acting only across the thin annular area of the tube cross section which is practically negligible.

Third, the present valve 2i is designed to close at an acute angle to the valve seat l0. Thus, at low flows, when the valve is operating close to its seat, a given linear change in valve position gives less change in area, providing the proper sensitivity.

' The seat itself has a nozzle contour which makes possible the short overall heightpf the unit. An expansion section is unnecessary with this type of nozzle, and it is only necessary to have a clear space on the atmosphere side of the valve.

In addition to the automatic control the present valve is equipped with a manual control which may be brought into operation at any time. This mechanism is probably best shown in Figures 7, 8 and 9 and includes a. rod 04 having an operating knob 65 provided at one end thereof and an engaging hook 66 formed by leaf spring members 61 and 68 attached at the opposite end of the rod 64 for engaging a flange 69 formed on the main valve 2|. The rod 64 is movable within a channel 10 formed in the casing i5 and passes through a locking member ll positioned within the channel ID. The rod 64 may be held in adiusted position by adjusting a fastening nut 12 so as to tighten flanged portions I 3 of the locking member II about the rod 64, thus holding the same in the adjusted position. The dance a constant pressure ratio control rather than constant pressure differential control. The arrangement shown in Figure 6 is otherwise substantially the same as that shown in Figure 5 and like numerals indicate like parts. However, insteadof the spring 53 and cup-like member 5| as shown in Figure 5, there is provided an evacuated bellows I9 which is positioned concentric with the bellows 48 and surrounds the same as shown in Figure 6. The sealing plate 41 in the latter arrangement forms one end of the bellows I9 and a frusto pyramidal end plate 80 forms the opposite end of the bellows i9 and 46 From this arrangement it will be seen that the ratio of the areas of'the two bellows 48 and 19 will detergiine the maximum pressure ratio at which the ut will tend to open and close the valve 51 as previously described. Thus in the operation of the second form of my invention upon the plane climbing to the 18,000 foot level as previously described, or upon the same reaching the predetermined atmospheric pressure range for operation of the constant pressure ratio control, the evacuated bellows 35 will have opened the valve 39 to its full open position and the constant ratio control bellows arrangement 46 and 19 will tend to open the valve 51 upon the ratio between cabin pressure and atmospheric pressure exceeding a predetermined value causing an adjustment of such pressures to the desired point. The advantage of the latter arrangement over the constant differential pressure control such as first described will be readily apparent when it is realized that at exceedingly high altitudes due to the rarifled atmosphere encountered the capacity of the normal supercharger having caorder to avoid this condition the latter constant ratio control has been provided.

Although only two embodiments of the invention have been illustrated anddescribed, various changes in the form and relative arrangement of the parts, which will now appear to those skilled in the art, may be made without departing from the scope of the invention. Reference is, therefore, to be had to the appended claims for a definition of the limits of the invention.

What is claimed is:

1. A mechanism to control aircraft cabin pressure, comprising, in combination, a cylindrical gate valve, a second cylinder surrounding said gate valve, a nozzle mounted at one end of said second cylinder, said second cylinder having openings to the cabin at the circumferental edge of the nozzle, said nozzle having an area normal to the airstream progressively decreasing from said circumferential edge so as to smoothly accelerate the air flow from said cabin, and said nozzle arranged as a valve seat for cooperating with one end of said cylindrical gate valve, said one end of said gate valve being formed with a substantially knife-like edge for contacting said nozzle, said valve including an air motor piston formed a part of said valve, said piston projecting laterally frc-m said valve member and slidably mounted in the second cylinder, and air power means for operatively adjusting said piston so as to regulate said valve.

2. A mechanism to control aircraft cabin pressure, comprising, in combination, a main valve for regulating the pressure within said cabin, a cylinder having a fixed bleed orifice leading therefrom to atmosphere, an air motor piston operatively connected to said main valve and slidably mounted within said cylinder for'controlling the movement of said main valve, said cylinder having an opening to cabin pressure, said opening and fixed bleed arranged so that said air motor piston has cabin pressure acting at one side thereof for opening said main valve and atmospheric static pressure acting at the opposite side through said fixed bleed orifice, spring means biasing said main valve in a direction opposing the force of said cabin pressure, whereby airflow through said fixed bleed orifice in response to movement of said air motor piston will tend to oppose movement of said main valve for effecting the stable control thereof, and control means for opening the aforesaid opposite side of said piston to cabin pressure in response to a cabin pressure in excess of a predetermined value.

3. A mechanism to control aircraft cabin pressure, comprising, in combination, a main valve for regulating the pressure within said cabin, a cylinder having a fixed bleed orifice leading therefrom, an air motor piston operatively connected to said main valve and slidably mounted within said cylinder for controlling the movement of said main valve, said air motor piston having cabin pressure acting at one side thereof for opening said main valve and atmospheric static pressure acting at the opposite side through said fixed bleed orifice, spring means biasing said main valve in a direction opposing the force of said cabin pressure, whereby airflow through said fixed bleed orifice in response to movement of said air motor piston will tend to oppose movement of said main valve for effecting the stable control thereof, an auxiliary control valve for opening the opposite side of said piston to cabin pressure, and cabin pressure responsive means for opening said auxiliary control valve at a predetermined minimum l0 cabin pressure for causing said air motor piston to actuate said main valve in a valve closing direc- 4. A mechanism to control aircraft cabin pressure, comprising, in combination, a main valve for regulating the pressure within. said cabin, a cylinder having a fixed bleed orifice leading therefrom, an air motor piston operatively connected to said main valve and slidably mounted within said cylinder. for controlling the movement of said main valve, said air motor piston having cabin pressure acting at one side thereof for opening said main valve and atmospheric static pressure acting at the opposite side through said fixed bleed orifice, and spring means biasing said main valve in a direction opposing the force of said cabin pressure, whereby airflow through said fixed bleed orifice in response to movement of said air motor piston will tend to oppose movement of said main valve for effecting the stable control thereof, a first auxiliary contro1 valve for opening the opposite side of said piston to cabin pressure, and cabin pressure responsive means for v opening said first auxiliary control valve at a predetermined minimum cabin pressure for causing said air motor piston to actuate said main valve in a valve closing direction, and a second auxiliary control valve for opening said opposite side of said air motor piston to atmospheric pressure, and differential pressure responsive means for opening said second auxiliary control valve at a predetermined maximum difference between cabin and atmospheric pressures for causing said air motor piston to actuate said main valve in a valve opening direction for decreasing the said difference in pressures.

5. The combination, comprising, a cabin pressure control valve, a piston for operating said cabin pressure control valve, a chamber, said piston slidably mounted in said chamber, said piston open at one side to cabin pressure, a fixed jet for connecting said chamber to atmospheric pressure so as to apply atmospheric pressure to the other side of said piston, said chamber having an orifice opening said chamber to cabin pressure so as to apply cabin pressure to said other side of said piston, a valve controlling said orifice, and cabin pressure responsive means for regulating said valve in such amanner as to open said orifice in response to a cabin pressure in excess of a predetermined value for applying said cabin pressure so as to bias said piston in one direction, and spring tension means augmenting the biasing force applied to said piston in said one direction, and said cabin pressure exerting a force upon said one side of said piston for biasing said piston in an opposite direction upon application of atmospheric pressure to said other side, whereby regulation of said cabin pressure contro1 valve may be eii'ected by said cabin pressure responsive means.

6. A mechanism to control aircraft cabin pressure, comprising, in combination, a cylindrical gate valve, an annular nozzle, a casing surrounding said nozzle at its air inlet side, said casing having openings therein to the cabin at the circumferential edge of said nozzle, said nozzle having a surface area normal to the airstream progressively decreasing from said circumferential edge so as to form a cabin air outlet opening to smoothly accelerate the air flow from said cabin, said nozzle arranged as a valve seat for cooperating with one end of said cylindrical gate valve, said one end of said gate valve being formed with a substantially knife like edge for contacting said a,441,oss

11 nozzle, and pressure responsive meansfor operatively adjusting said valve for controlling the outflow of air from the cabin.

7. A mechanism to control aircraft cabin pressure. comprising, in combination, a cylindrical gate valve, a second cylinder surrounding said gate valve. a piston formed integral with said valve and projecting laterally therefrom, said piston slidably mounted in said second cylinder for effecting movement of said gate valve, an annular nozzle positioned at one end of said second cylinder, said second cylinder having openings to the cabin at the circumferential edge oi the nozzle, said nozzle having a surface area normal to the airstreani progressively decreasing from said circumierential edge so as to form a cabin outlet opening to smoothly accelerate the air flow from the cabin, said nozzle arranged as a valve seat for cooperating with one end of said cylindrical gate valve, said one end of said gate valve having a substantially knii'e like edge for contacting said nozzle within the opening formed by the pro-' gressively decreasing surface area thereof, and cabin pressure responsive means for controlling the operation or said piston and the outflow oi air from the cabin through said nozzle.

, 8. A mechanism to control aircraft cabin pressure, comprising, in combination, valve means including a valve seat, a hollow valve member open at opposite ends and longitudinally movable in relation to said valve seat, said valve means having an air outlet opening controlled by sald'valve member, one end of said valve member being formed with a substantially knife like edge to contact said valve seat. a piston formed integral with said valve member and projecting laterally therefrom, a chamber open at one end and within which said piston is slidably mounted, a spring acting solely upon said piston for biasing the valve member in a valve closing direction and in opposition to cabin pressure applied to one side oi said piston through the open one end of said chamber, means for applying a variable fluid pressure to another side of said piston to a kment the biasing tom of said spring, and means for controlling the application of the variable fluid pressure to said piston.

9. The combination defined by claim 8 in which the last mentioned control means is responsive to cabin pressure.

10. The combination defined by claim 8 in l which the last mentioned control means is re- 12 sp nsivc to changes in the diiierence between cabin and atmospheric pressures.

11. The combination defined by claim 8 in which the last mentioned control means is responsive to changes in a predetermined ratio between cabin and atmospheric pressures.

12. The combination defined by claim 8 in which the last mentioned control means includes first control means for regulating the application oi the fluid pressure to said piston in response to cabin pressure, and second control means operative upon a predetermined differential between cabin and atmospheric pressures for controlling the application of the fluid pressure to said piston. 13. The combination defined by claim 8 in which the last mentioned control means includes first control means for regulating the application oi the fluid pressure to said piston in response to cabin pressure, and second control means operative upon a predetermined ratio between cabin and atmospheric pressures for controlling the application of the fluid pressureto said piston.

WALTER D. TEAGUE, JR.

REFERENCES CITED The following references are of record in the file of this patent:

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